This invention relates generally to metal detection apparatus, and more particularly the invention relates to a system which detects signals emitted from a metal object such as an underground pipe and particularly to a vector positional display for use therein.
In the construction and utility maintenance fields, the ability to trace underground metal and underground piping has been a needed requirement for both safety and maintenance purposes. Currently available equipment to do this job uses very low frequency systems for detection and tracing. These frequencies may start at 1 kHz and go up as high as 490 kHz.
The ability to detect and trace underground piping is greatly affected by the environment that exists at the time of detection. If the ground is very wet or is made of different combinations of earth, erroneous results may occur. If the underground pipe or metal contains an insulating gasket, this may limit the distance at which the pipe can be traced due to the gasket acting like a very low value capacitor. This capacitor is a high impedance to the very low frequency signals, thus preventing them from jumping across the gasket. In addition, the ability to couple the low frequency energy to the underground metal or pipe becomes very difficult. The extreme low frequency makes necessary a very high voltage for the pipe to emit enough signal to be detected.
Various types of display devices are used in utility locating equipment. Most of these displays are for single point location. The present invention is a display which is intended for use with systems that can deliver multiple target information. This makes possible the display of underground pipe branching. In addition, a variable resolution capability allows better tracing of close proximity.
The vector positional display in accordance with the invention responds to a counter driven by a system reference clock with the accumulated count being indicative of position of a sensor array detector with respect to the underground object and to resolution decoders for the count by which different distance resolutions can be provided. The counter further responds to a data strobe signal such as a zero crossing detector by energizing one or more lights for indicating the position of one or more underground metals and pipes relative to the antenna array detector.
More particularly, the variable resolution vector position display comprises four subsystems. These include a display slot counter, a resolution multiplexer, a display decoder, and a multi pixel unit display. The display slot counter is a divide by n bit counter, where n is the number of stages required for the particular application resolution. The three most significant bits of the counter are used to synchronize external systems such as a signal sensor electronic switch. The input to the slot counter comes from a reference clock supplied by the system that the display unit is connected to. The output of the slot counter feeds a data buffer. The buffer isolates the resolution decoders to reduce loading effects on the slot counter outputs. The output of the data buffer feeds the inputs of the resolution decoders. The number of resolution decoders is dependent on the application. In the illustrative embodiment, three resolution decoders are used. The resolution decoders define the vector display output display resolution. For the example shown here the three resolution decoders are: times one (180xc2x0), times two (90xc2x0), and times four (45xc2x0). The resolution value for the decoder is determined by decoding different bit outputs from the slot counter. Outputs from the resolution decoders feed a multiplexer. The number of inputs on this multiplexer is determined by the number of output lines from the resolution-decoders, and the number of resolution decoders used in the system. The multiplexer allows the selection of the various resolutions. The output of the multiplexer feeds the main display decoder. This decoder converts the data from the resolution multiplexers to the data required for the display array. The display array can be made up of any type of visual display device. LEDs, LCDs, plasma, and vacuum fluorescent displays, can be handled by the system.